There has been known a technology in which a diesel particulate filter (or NOx catalyst) or the like is arranged as an exhaust gas cleaning device (after-treatment device) in an exhaust gas path of a diesel engine and in which exhaust gas exhausted from the diesel engine is cleaned by the diesel particulate filter (or NOx catalyst) or the like (see patent literature 1, patent literature 2, and patent literature 3). Further, there has been also known a technology in which a filter case (inner case) is fitted in a casing (outer case) and in which a particulate filter is arranged in the filter case (see patent literature 4).